[0/2] audit: Further reduce syscall latency

Message

Haakon Bugge Dec. 12, 2023, 10:28 a.m. UTC

On an Intel Cascade Lake, booted with "audit=0" and "mitigations=off",
syscall latency in nanoseconds over 10 reboots and 5 runs is:

getpid() latency:
Boot parameters           kernel            min    avg     max      pstdev
                                           (ns)   (ns)    (ns)        (ns)

audit=0, mitigations=off  v6.6-rc4           55    55       58    0.797245
audit=1, mitigations=off  v6.6-rc4          205   210      227    6.402000
audit=1, mitigations=off  v6.6-rc4+[1]      203   203      209    0.954149
audit=1, mitigations=off  v6.6-rc4+[1]+[2]  173   173      178    0.884534

So, audit contributes significantly to the cost of a system call.

This series, hopefully applicable to audit/next (if accepted), reduces
the syscall latency by a decent 21% on an Intel Cascade Lake system.

The above numbers are derived using the same methodology as mentioned
in the commit messages.

The first commit, "audit: Vary struct audit_entry alignment", fixes a
huge L1D miss ratio and greatly reduces the variability on the three
metrics, nanoseconds per syscall, L1D misses per syscall, and
Instructions per Cycle (ipc). It does not greatly reduce on the
syscall latency, only a decent 3.5% reduction. But, it serves as a
pre-requisite for the second commit, "audit: Apply codegen
optimizations".

Please review.

Håkon Bugge (2):
[1] audit: Vary struct audit_entry alignment
[2] audit: Apply codegen optimizations

 kernel/auditfilter.c | 14 +++++++++++---
 kernel/auditsc.c     |  2 ++
 2 files changed, 13 insertions(+), 3 deletions(-)

--
2.39.3